Overview
Description and rationale
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Borrow and Payback has been modelled in predecessors to Source, such as IQQM and MSM, for many years. The concepts in these models have been updated and enhanced to suit the needs of Source.
Version
Source version number 2number 4.191.1.
Dependencies
The model configuration in Source must include at least one Ownership System with at least two Owners for borrow and payback to be modelled.
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Automatically included with the full version of Source.
Structure & processes
Theory
Introduction
The Murray Darling Basin Agreementenables the operators in the River Murray to exchange the ownership of volumes of water between the states of New South Wales (NSW) and Victoria when the lending state has water surplus to its requirements. An example of this is when state owned tributary inflows are greater than expected. These excess tributary flows result in a state’s share of water in the river being surplus to that required to meet to meet its ordered requirements. Where possible, this excess water is utilised by the other state (owner) and the amount of water that needs to be released from storage is reduced. The water used by the other state (owner) is termed a borrow and is reconciled against the state’s water share. In the case of the River Murray, payback and account balances are reconciled at Lake Victoria.
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- Inflow and confluence nodes
- Wetland hydraulic connectors
- Loss nodes
- Supply point nodes
- Controlled splitter nodes
- Storage nodes (Weir upstream reach not included)
- Links
Borrow and Payback accounting occurs mainly during the flow distribution phase, although some aspects of Borrow and Payback are also considered in the order phase. For a weir node, Borrow and Payback only occurs in the weir storage component and not the upstream reach.
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Table 1. Assumptions and constraints
| No | Assumption/constraint |
|---|---|
| 1 | An ownership system must have a global borrow and payback system. |
| 2 | An ownership system’s global borrow and payback distribution hierarchy applies in all storages where there is no local borrow and payback system. |
| 3 | Borrow and payback systems only operate when ownership is enabled. |
| 4 | A borrow can occur anywhere in an ownership system when one or more owners has insufficient water to meet requirements. |
| 5 | When a global borrow and payback system is reconciled/paid back at a storage, the payback storage must maintain a local borrow and payback system. |
| 6 | For payback at a storage, owners are checked to see if they have to forfeit lending credit if they do not have enough airspace available. This is to ensure that the owner has enough capacity to be repaid. |
| 7 | When a global borrow and payback system is reconciled/paid back at a storage, all owners in the system must payback water at the same storage. |
| 8 | Borrow and payback accounting will occur prior to resource assessment. Resource assessment and accounting must consider the total sum of all borrows in the model, and thus includes:
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| 9 | The borrow network for the global borrow and payback system must be complete. That is, there must be a connection between each owner and every other owner (the connection can be made at any priority level). |
| 10 | The borrow network for sharing a system constraint must be complete. An operator is not going to refuse service to an owner if there is surplus capacity available to use to serve them. |
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For more details on payback at a storage see Ownership in Storages - SRGOwner Capacity Share Proportion Method.
Time step: Resource Assessment – Water Accounting Phase
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